Method for blending powder grains



March 16, 1948. c. N. HICKMAN 2,437,694

' METHOD FOR BLENDING POWDER GRAINS Filed May 15, 1946 2 Sheets-Sheet 1a l7 l2 I Blur Bil Ll: e N- H-i cum-an M r 16, 1948. c. N. HICKM'AN I2,437,694

METHOD FOR BLENDING POWDER GRAINS Filed May 15, 1946 2 Sheets-Sheet 2 1P i 51. EL.

awe/WM Blur an; e N. HiuKm-nn- Patented Mar. 16, 1948 UNI TE-D -:STAT ESPATENT OFF-ICE -M-ETHGD FOR, BLENDING POWDER GRAINS *Cia'r'ence" N.Hickman, Jackson Heigh ta'Y N. Y,

*assignor to U nite'dstatcs' 'ofjfA'iiiri'oa, as represented by theSecretary of War Application May 15, 1946, Serial No.-669,765

(Granted under the act 'of March 3, 1883, as

4 "Claims.

operation in powder manufacturing, Without which uniformity l'inb'allistic performance could not be obtainedbe'cause it --is impossibleto "accurately control the chemical manufacturing processes so'tha'teach batch of powder will have exactly the same pr'eperties. n powderindexer lot, 1 as made up for service useeonsi'stspf 50,000 pounds ormore of owder and-in order' to make up such a lot it-i'sinece'ss'ary' touse dried-grains .fromralnumber of difierent powder-batches. The

:grain's'lirom the different powder batches mudt be thoroughly mixed orhlendedto g-ive uniformity throughoutthe lot. g

The blending of pwder, as a-cco ished by the prior art, isica'rriedoutin blend-1 g' towers.

One type of blending" tower consists foi 'a series of .bins arranged inhorizontal groups; the groups being positioned in verticalrelation-toeachother. The bins of each groupmay be in polygonal relation, each bin having a trapbrgatevalve rac ing toward'the center ofthe group. In blending, the top group of fthe bins is 'cha'rgeti withthe required amount of powder from'eachof theselected batches. The trapor gate valves are opened simultaneously and-the powder from all f thebins falls to the'nextgroup in a single stream which divides aboutequally into the 'bins of the next group. This operation is continuedfrom group to group and the powderis finally=draiwn ofi througharhopperlatthe bottom'of the "blending. tower. In 1 other blendingtowers the powder in the first blending bin is released .-to fall over adistribution-cone before enteringthe nextlower group of bins. Thisdistribution cone improves the blending of the powder. If a' highdegreeof uniformity is desired, however, it is necessary to run the powderthrough the blending tower at number of times. One characteristicdisadvan tage of this prior art blending process is the hazard involveddue to the development of static electricity. Although apparatushas'be'endesigned to remove the electric charge from the parts of thesystem, the addition of this apparatus rather complicates the structureand is not entirely satisfactory. a

amended April 30, 1928; 370 O. 'G. 757) In one type of rocket motor, asmany as 30 individual grains, each about 5 inches'in length andabout V8inch-in diameter, are used; Different loading performances have beenfound, traceable only to'noh uniformity in the powder mtg-fromwhich'theloadihgs weremade, i. e., to inadequate blending of the powder.Because of the tremendous hazards involved, it has not been possible toblend powders of this larger grain size with the -Iiie'chanical meansknown to the prior-art, hence, it is an object of this invention toprovide 'a inetho'd and apparatus for blending powders of /8 inch'grainsize or larger which is non-hazardous and which produces a higherdegree of uniformity in blending than has been obtainable heretofore byany of the methods known to the prior art.

The specific-natiire of the invention as well as other objects andadvantages thereof will clearly appear froma description ofa preferredembodimerit as shown in the accompanying drawings in which:

Fig. '1 is a vertical -section through the blend ing apparatus isdescribed.

Fig. 2 shows an alternate arrangement for the recirculating system.

This invention consists essentially of a method of and an apparatus formixing powder grains by means of the circulation of an electrolyticmixing medium of lower specific gravity than the powder through a 'vatcontaining the powder grains, at a sufic'ient velocity to displace themwith respect to each other, the preferred medium for this applicationbeing water which has been saturated with nitro-glycerine ito preventany of the nitro-glycerine content of the powder from being absorbed bythe water. The powder grains to be mixed are placed in avat, the liquidmixing medium 'is added until it rises considerably above the top of thegrains and then a jet of the liquid is ejectedupwar'dly through thebottom of the vat at sufliciently high velocity to break through thesurfaceof the liquid and fan out in a fountain-like manner, The grainslocated in the path ofthe jet are carried upwardly and out wardly alongwith the jet dropping back in a haphazard manner, thus being verythoroughly dispersed or mixed.

The apparatus consists of a base i on which is mounted a vat 3 in theform of an ellipsoid generated by revolution of an ellipse about itsconjugate axis, the axis being disposed, vertically. The vat 3 containswater saturated with nitroglycerine. charging door 5 is provided in theupper part of the Vet 3' and-a discharging door 1 near the bottom. Arecirculating system is provided, the system consisting of an outletpipe ll, a pump II and an inlet pipe l2 terminating in a nozzle l3adjacent the bottom of and in the vertical axis of the vat through whicha water jet I6 is forced by the pump ll. Outlet pipe i is covered by abaflle l4 and a screen l5 which prevents powder grains 24 from gatheringaround or passing into the outlet line I!) of the recirculating system.

The ellipsoidal form of vat is especially advantageous for thisapplication since the tendency therein of the grains to slide toward thecenter without excessive crowding is uniform in all directions; however,any form of vat having a declivitous fioor sloping toward a low point atwhich the nozzle can be located may be used.

A drain pipe IT with a valve [8 is provided for draining water from thevat 3 into a storage reservoir (not shown). A screen I9 covers drainpipe I! to prevent egress of powder grains 24.

For some applications it may be desirable to make use of gravity feed ofthe water, thereby maintaining a constant head and as a result, constantpressure at the nozzle l3 and uniform fountain effect in the vat. Thisconstruction is illustrated schematically in Fig. 2 in which a standpipe30 would provide the necessary head. A feed line 3| leads from standpipe30 to nozzle l3 with a valve 32 inserted to control the flow. Anoverflow line 33 and a drain line 34 with a shutoff 35, lead from vat 3to a storage tank 36.

, Standpipe 30 is also provided with an overflow line 31 leading tostorage tank 36. A pump 38 supplies water to standpipe 30 through a feedline 39.

In operation, a lot of powder, consisting of a predetermined quantity ofpowder from each of the batches to be blended is placed in the vat andsufficient water, saturated with nitro-glycerine, is added to fill thevat to a point well above the top of the powder grains and the outletI0. Charging door 5 is then closed and pump Ii started, forcing a jet ofwater from the nozzle l3 to rise vertically upward from the bottom ofthe vat breaking through the surface of the water and fanning out in afountain-like manner before falling back. As the grains in the middle ofthe vat 3, i. e., in the path of the jet l6, are carried upward andspread out on top, the mass settles toward the center so that eventuallyall grains are recirculated or redistributed, hence a high degree ofdispersion is attained with a consequent uniformity of blend. By usingan electrolytic liquid such as water as a circulating medium, thedangers resulting from static charges developed in blending towers areavoided and by saturating this water with nitro-glycerine, thenitro-glycerine content of the powder grains is maintained undiminished.

In the manufacture of service smokeless powder, particularly single-baseservice smokeless powder, the drying operation may be carried out bycirculating warm waterrather than air through the powder grains. It maybe desirable to continue the drying process for the removal of volatilesin the nitro-cellulose powder, utilizing the blending process of thisinvention, thus combining steps in manufacture. However, notwithstandingthis possible combination of operations, the superior blending obtainedby this process would warrant the substitution of this step inmanufacture for the conventional blending process as carried out intowers, particularly in view of the fact that blending towers nowutilized are inadequate for blending powder grains of a size necessaryfor some rocket propellent applications. A heating coil as indicated at2| could be used to warm the mixing medium when desired.

While the preferred embodiment as above described is especially adaptedfor this application, modifications such as would occur to anyoneskilled in the art may be made without departing from the spirit of theinvention.

. It is apparent from the description and drawrings that this inventionprovides a method and apparatus whereby very large size grains ofsmokeless powder can be safely and thoroughly .mixed, resulting in animproved blending of various batches of powder into a final uniform:index or lot.

I claim:

1. A method of blending powder grains includ- .ing the steps of placingthe powder grains to be blended in a vat, adding a liquid of lowerspecific gravity than the powder grains in quantity sufficient to riseto a substantial height above the grains, said liquid beingsubstantially a non- :solvent with respect to said grains, andcirculating said liquid, including projecting a jet of the liquidupwardly from the bottom of the vat among the grains whereby the grainsin the path of the jet are propelled upwardly into changed relation withrespect to the other grains in the vat.

2. A method of blending smokeless powder grains including the steps ofplacing the powder grains to be blended in a vat, adding water saturatedwith nitroglycerine, said water being added in quantity sufiicient torise to a substantial height above the grains, and circulating saidwater by withdrawing it from the vat and projecting it upwardly throughthe bottom of the vat with sumcient velocity to break through thesurface and fan out in a fountain-like manner, whereby the grains in thepath of the jet are propelled upwardly above the surface of the liquidto fall back in a haphazard manner on top of the other grains therein.

3. A method of mixing and drying particles of solid material containinga volatile constituent,

including the steps of placing the solid particles in a vat, addingenough liquid of lower specific gravity than the solid particles inquantity sufiicient to rise to a substantial height above the solidparticles, said liquid being substantially a non-solvent with respect tothe particles, maintaining said liquid at a temperature capable ofvolatilizing the volatile constituents thereof and projecting a jet ofthe liquid upwardly from the bottom of the vat among the particleswhereby the particles in the path of said jet are moved into changedrelation with respect to the other particles in the vat.

4. The method of blending propellent powder grains which comprisesplacing in a vat the said propellent powder grains and a liquid of lowerspecific gravity than the powder grains, said liquid being substantiallya non-solvent for the constituents of the powder grains and present insufiicient quantity to rise above said grains; and circulating saidliquid by withdrawing a portion thereof from the vat and injecting saidportion in the form of a high velocity stream vertically upwards throughpowder grains and liquid in said vat, the velocity of said stream beingsufficient to thoroughly mix the said grains.

CLARENCE N. HICKMAN.

(Iteferences on following page) Pontoppidan "Feb. 8, 1927 1 537,408

Name Date Kelly Mar. 26, 1929 Bloom Dec. 15, 1931 Soderholm Jan. 19,1937 Alexander June 26, 1945 FOREIGN PATENTS Country Date Germany Nov.11, 1933 Great Britain June 20, 1941

